The present invention relates to an oxidation process and in particular to a process for the oxidation of unsaturated hydrocarbons in the presence of catalyst under heterogeneous conditions.
It is well known that the epoxidation of unsaturated hydrocarbons e.g. olefinic compounds, with various oxidants such as hydrogen peroxide may be effectively catalyzed by certain synthetic zeolites containing metal atoms such as titanium atoms (see, for example, U.S. Pat. No. 4,833,260).
Various process modifications have been proposed to improve the conversion and selectivity of these oxidation reactions. U.S. Pat. No. 4,824,976 proposes that the non-selective ring-opening reactions which take place when epoxidation is performed in a protic medium such as water or alcohol may be suppressed by treating the catalyst prior to the reaction or during the reaction with a suitable acid neutralising agent. The neutralising agent is said to neutralise acid groups on the catalyst surface which tend to promote by-product formation
U.S. Pat. No. 5,675,026 proposes the addition of neutral- or acid-reactive salts to the catalyst before or during the reaction to improve catalyst activity. U.S. Pat. No. 4,483,996 discloses a process for the conversion of olefins to olefin oxides and ketones. The process utilises a thallous catalyst, with molecular oxygen as oxidant in an aqueous carbon dioxide solvent. U.S. Pat. No. 5,591,875 proposes an epoxidation process which
utilises a chelating agent to reduce the catalysts tendency to non-selectively decompose the hydrogen peroxide oxidant used. EP 0 385 631 A1 describes an oxidation process for the conversion of olefins to glycols utilising oxygen and carbon dioxide as reactants under supercritical conditions. A heterogeneous copper containing catalyst is proposed. U.S. Pat. No. 5,646,314 proposes performing the oxidation reaction in the presence of nonbasic salts in order to improve selectivity.
Furthermore it has long been recognised that metal containing zeolite catalysts rapidly become deactivated in use. There have been a number of methods developed to counter this deactivation and/or to regenerate the catalyst after use. U.S. Pat. No. 5,741,749 proposes a the regeneration of a titanium containing molecular sieve oxidation catalyst by treatment with a gas stream comprising specific amounts of molecular oxygen. WO 98/18555 proposes the regeneration of a titanium silicalite catalyst with a liquid solution of an oxidising agent. WO 98/18556 proposes the regeneration of a titanium silicalite catalyst under a specific gas flow
In U.S. Pat. No. 5,210,336 a process is described for the conversion of olefins to glycols utilising a CuI/Cu2O catalyst. The reaction is undertaken in the presence of carbon dioxide which acts as a solvent and a co-reactant, under supercritical conditions.
There are a number of problems with the processes of the prior art. Conversions and selectivities for the various reactions are in general still low or require additional process modifications which incur additional costs. Frequently the catalyst systems utilised require special treatments and/or frequent regeneration in order to maintain catalyst activity.